The present invention relates to a positive type photosensitive composition. In more detail, the invention relates to the positive type photosensitive compositions to be used for making positive type image-forming materials by coating onto the supporter and is utilized mainly for printing plate-making materials, draft-duplicating materials and the like.
As the conventional photosensitive compositions used for the positive type image-forming materials, there are:
(1) Composition consisting of o-quinonediazide compound
This is a composition consisting of o-quinonediazide compound and alkali-soluble resin such as Novolak resin and a phenomenon wherein o-quinonediazide changes to alkali-soluble substance upon the irradiation of light is utilized (For example, this can be seen in Japanese Unexamined Patent Publication No. Sho 50-125806, Sho 61-5251, etc.).
(2) Composition consisting of photosensitive diazonium salt and water-soluble resin
This is a composition consisting of photosensitive diazonium salt and water-soluble resins such as poly(vinyl alcohol), diacetoneacrylamide-acrylamide copolymer, etc. and a phenomenon wherein photosensitive diazonium salt and water-soluble resin give rise to the coupling reaction under the atmosphere of alkali to become water-insoluble is utilized (For example, this can be seen in Japanese Unexamined Patent Publication No. Sho 56-101141, Sho 56-101144, Sho 57-72140, Sho 57-191632, etc.).
However, these conventional photosensitive compositions have following problems, That is,
1 Since both (1) and (2) use alkali solution for the development, the problem of safety during the development operation and the pollution problem in the treatment of spent water are in danger of accurrence. Moreover, the development treatment with ammonia vapor is also possible in (2), whereby the strong smell of ammonia worsens the operation environment remarkably.
2 There remains the color of o-quinonediazide or the decomposed compound thereof in the images formed by (1) and there is a peculiar coloration due to the coupling reaction in (2). For these reasons, it is difficult to obtain colored images of arbitrary color in both (1) and (2), even if added coloring agent.
The purpose of the invention is to provide a positive type photosensitive composition for making positive type image-forming material wherein the development is possible with water or warm water and there do not occur the tinting due to photosensitive component or the decomposed product thereof, the coloration resulting from the image-forming reaction and the like.
As a result of diligent studies on a novel positive type photosensitive composition developable with water or warm water, the inventors have found a phenomenon wherein the positive type photosensitive composition can be obtained by using water-soluble photocrosslinking agent (for example, one shown in Japanese Patent Publication No. Sho 44-28725) having been used for negative type photosensitive composition conventionally. Namely, the phenomenon wherein the positive images are obtained by exposing a photosensitive layer coated with a composition consisting of water-soluble photocrosslinking agent, water-soluble resin and synthetic resin emulsion onto the supporter to light through positive manuscript, by immersing into water and by rubbing with a sponge has been found. Moreover, in the images thus obtained, the tinting due to photosensitive component and the coloration accompanied with image-forming reaction were not caused at all. The mechanism of this phenomenon is considered as follows:
Exposed areas
Through the exposure to active rays, the water-soluble photocrosslinking agent and the water-soluble resin in the photosensitive layer are crosslinked photochemically. And, when immersing, this photocrosslinking component swells easily to soften the photosensitive layer of this portion. Moreover, it lowers the adhesion to the supporter. Consequently, those portions are removed easily from the supporter by rubbing with a sponge, etc.
Nonexposed areas
When immersed into water, the greater part of water-soluble photocrosslinking agent and water-soluble resin in the photosensitive layer is dissolved out, but the photosensitive layer exhibits no changes such as swelling, softening, etc. and the adhesion to the supporter does also not change. Consequently, it is not removed from the supporter even if rubbed. Moreover, since the greater part of water-soluble photocrosslinking agent in the photosensitive layer is dissolved out, the remaining photosensitive layer is colorless.
The invention relates to the positive type photosensitive composition utilized the phenomenon aforementioned.